Method of processing female spline of hub unit for supporting wheel

ABSTRACT

In a method of processing a female spline of a hub unit for supporting a wheel, a hole  3   a  which is formed to be cylindrical is provided on a shaft portion  3   c  of a hub unit  103  before plastically deforming by caulking (or clinching), and after the plastically deforming by caulking (or clinching), a female spline is formed on the hole  3   a  by semi-dry or dry broaching. The hole  3   a  which is formed to be cylindrical after plastically deforming by caulking (or clinching) has the form that the size is greater at a portion nearer a portion  3   d  plastically deforming by caulking (or clinching) of the shaft portion  3   c  for an estimated amount of contraction caused by the plastically deforming by caulking (or clinching) or the press-fitting of an inner race element.

TECHNICAL FIELD

The present invention relates to a hub unit for supporting a wheel whichis attached to an automobile, or the like, and particularly, to a methodof processing a female spline which is formed on a shaft portion of thishub unit.

BACKGROUND ART

In a conventional method of changing the form of a female spline of ahub unit and of processing the female spline, as shown in FIG. 11, a jig15 is abutted against an inner wall of a spline hole 3 a which is formedon a hub shaft portion 3 c of a work 103 for a hub unit to effectplastically deforming by caulking (or clinching) so that a material isprevented from being extruded (see, for example, Japanese PatentApplication Laid-Open No. 2001-162338). This arrangement is effective inincrease of the axial force. In FIG. 11, a reference numeral 16 denotesan outer race which is fitted on the hub shaft portion 3 c throughbearings 18; and 17 an inner race element to be press-fitted on the hubshaft portion 3 c.

Also, in the conventional method of forming and processing a femalespline of a hub unit, as shown in FIG. 12, there is provided a portionwhich is extended in midair between a female spline portion 3 e and aportion 3 to be plastically deformed formed on the hub shaft portion 3 cof the work 103 for the hub unit, as a buffer portion X (see, forexample, Japanese Patent Application Laid-Open No. 2002-29210). Thisarrangement is effective in suppressing deformation of the female splineportion caused by plastically deforming.

Further in the conventional method of processing a female spline of ahub unit, the female spline of the hub unit is processed by broaching(see, for example, Japanese Patent Application Laid-Open No.2002-61661). This arrangement is advantageous in regulating the surfaceroughness of the female spline. Still further, in this processingmethod, though a hub unit is different from that of the presentinvention since comprising a hub wheel and a constant velocity jointcombined with each other, a female spline is in some case formed bymachine work such as broaching, hardening processing, or polishing (see,for example, Japanese Patent Application Laid-Open No. 2002-301407).

Further, in order to prevent the diameter of a serration from beingcontracted by plastically deforming, the female spline of the hub unitis subjected to broaching after the shaft portion is plasticallydeformed caulking (or clinching) (see, for example, Japanese PatentApplication Laid-Open Nos. 2002-283804 and 2002-89572).

However, in the processing method disclosed in the Japanese PatentApplication Laid-Open No. 2001-162338, out of the methods of processingthe female spline of the hub unit described above, it is practicallyimpossible to manufacture a jig 15 which is in contact with all of thesurfaces of the female spline because of a processing error of thefemale spline. As a result, there arises a problem that a surface of thespline with which the jig 15 is not in contact is exposed uponplastically deforming by caulking (or clinching) so that the form of thespline is not as designed.

In the method disclosed in Japanese Patent Application Laid-Open No.2002-29210, when the axial length of the hub unit is limited, it isrequired to reduce the length of the female spline portion 3 e. For thisreason, the length of a surface of contact between the female spline 3 eof the hub unit 103 and a female spline of the constant velocity jointis shortened, so that the torque transmission can not be carried outwith efficiency. That is, there is a problem that, when the hub unit isrequired to have a certain length of the female spline or when the hubunit has a comparatively small axial length, this processing method cannot be employed.

In the method disclosed in the Japanese Patent Application Laid-Open No.2002-283804 and the method disclosed in the Japanese Patent ApplicationLaid-Open No. 2002-89572, the female spline of the hub unit is subjectedto broaching after the shaft portion is plastically deformed by caulking(or clinching) so as to avoid the contraction of the diameter of theserration caused by the plastically deforming by caulking (orclinching). However, since neither semi-drying process nor dryingprocess is conducted, a washing step after the treatment can not beomitted. Also since the broaching is not carried out by shielding chips,when the hub unit incorporates therein an encoder formed of multipolarmagnet, there is a fear that the chips adhere to the encoder so as todeteriorate a rotation detecting function of a sensor which is used withthe encoder to make a set.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method of processinga female spline of a hub unit for supporting a wheel which can solve theproblems of the prior art described above, can process the female splinewith precision, and can omit a washing step after the treatment.

In order to achieve the above object, according to one aspect of thepresent invention, a bearing of which a hub shaft portion is formed bycutting with a hole extended in the axial direction, and after an innerrace thereof is fixed by plastically deforming by caulking (orclinching) to form a work for a hub unit, a female spline is formed onthe hole by semi-dry or dry broaching. It is preferable that the abovehole is formed to have a greater part for an estimated amount ofcontraction caused by the plastically deforming by caulking (orclinching) or the press-fitting of the inner race element at a portioncloser to a portion plastically deformed by caulking (or clinching) ofthe shaft portion.

According to another aspect of the present invention, the female splineis roughly processed by broaching on the shaft portion of the work for ahub, and then a bearing is fitted on the shaft portion and an outer endof an inner race of the bearing is fixed by plastically deforming bycaulking (or clinching) at an end of the shaft portion in the axialdirection. After that, the female spline is finished by semi-dry or drybroaching. The rough broaching of the females spline is preferablyperformed in the following manner. A ring is press-fitted on the shaftportion having a cylindrical hole of the hub unit or a part of the shaftportion is chucked, whereby this hole is made to have the form beingnarrower for an amount of contraction by plastically deforming bycaulking (or clinching), or press-fitting of the inner race element at aportion nearer the portion plastically deformed by caulking (orclinching) of the shaft portion. The broaching is carried out in thisstate.

By employing such a processing method as described above, it is possibleto prevent a lower part of the female spline hole from being swollen anddeformed, whereby the female spline can be formed with precision,without increasing the number of the processing steps.

In addition, the cost for finishing the female spline can be reduced, byconducting rough processing of the female spline beforehand.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view for showing a structure of a broachingwork related to the present invention, when a work for a hub unit isturned up;

FIG. 2 is a cross sectional view for showing a structure of thebroaching work related to the present invention, when a work for a hubunit is turned down;

FIG. 3A and FIG. 3B are for showing a cross section of the work for thehub unit prior to the broaching work, wherein FIG. 3A shows a shape of ahole for forming a spline before plastically deforming by caulking (orclinching), and FIG. 3B shows the shape after plastically deforming bycaulking (or clinching);

FIG. 4A and FIG. 4B are respectively whole and partial cross sectionalviews for showing a seal attached to the work for the hub unit;

FIG. 5 is a lateral sectional view for showing a state in which the workfor the hub unit is carried in during the broaching work related to thepresent invention;

FIG. 6 is a lateral sectional view for showing a state in which a toolis inserted through the work for the hub unit in the broaching work;

FIG. 7 is a lateral sectional view for showing a state in which a splineprocessing is carried out by broaching;

FIG. 8 is a lateral sectional view for showing a state before the hubunit is carried out after the broaching work;

FIG. 9A and FIG. 9B are cross sectional views for showing a roughprocessing for forming the spline of the work for the hub for hub unitformation, wherein FIG. 9A shows a state before the broaching work, andFIG. 9B shows a state after the broaching work;

FIG. 10A is a partial cross sectional view of the hub unit in the axialdirection, and FIGS. 10B to 10E are characteristic diagrams forrespectively showing deformation data of a spline hole of the hub unit;

FIG. 11 is a cross sectional view of a work for a hub unit for showing aconventional processing method of spline formation using a jig; and

FIG. 12 is a partial cross sectional view of a work for a hub unit forshowing a conventional method of forming and processing a spline byarranging a buffer portion between a spline portion and a portionplastically deforming by caulking (or clinching).

EMBODIMENT OF THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings.

Description will be made on a work 103 to be processed by a method ofthe present invention which will be specifically described in thefollowing with reference to FIGS. 3A and 3B. The work 103 comprises ahub 3 which integrally has a shaft portion 3 c and a flange 3 b forsupporting a wheel, an inner race element 17 which is press-fitted onthe hub shaft portion 3 c at a predetermined portion on the outerperiphery thereof, an outer race 16 which is concentric to the hub shaftportion 3 c and the inner race element 17 and distant therefrom in theradial direction to be opposed thereto and has a flange 16 a to beconnected and fixed to a knuckle of a suspension, and two rows of balls18 which are interposed between the inner periphery of the outer race 16and the outer peripheries of the shaft portion 3 c and the inner raceelement 17 and constitute a rolling bearing together with these members.This work 103 has been assembled in advance as a hub unit work. Acentral hole 3 a having a cylindrical form has been formed by grindingon the shaft portion 3 c, while the inner race element 17, afterpress-fitted on the shaft portion 3 c, has been fixed by plasticallydeforming a portion 3 d by caulking (or clinching) to keep the positionof the rolling bearing (FIG. 3B).

In the present specification, when the hub unit which is completed bythe method of the present invention is attached to the car body, the hubunit work is disposed to be turned up if a portion corresponding to aninside of the car is positioned in an upper part and a portioncorresponding to the outside of the car is in a lower part, while it isdisposed to be turned down in the opposite case.

FIG. 1 is a view of a broaching work according to an embodiment of thepresent invention, when a work for a hub unit is turned up. FIG. 2 is aview of a broaching work according to an embodiment of the presentinvention, when a work for a hub unit is turned down. FIG. 3A and FIG.3B are cross sectional views of the work for the hub unit prior to thebroaching work, wherein FIG. 3A shows a shape of a hole for forming aspline before plastically deforming by caulking (or clinching), and FIG.3B shows the shape of the hole for forming a spline after plasticallydeforming by caulking (or clinching). FIG. 4A and FIG. 4B arerespectively a whole cross sectional view and a partially enlarged crosssectional view of a seal attached to the work for the hub unit. FIG. 5is a lateral sectional view for showing a state in which the work forthe hub unit is carried in during the broaching work. FIG. 6 is alateral sectional view for showing a state in which a tool is insertedthrough the work for the hub unit in the broaching. FIG. 7 is a lateralsectional view for showing a state in which a spline processing iscarried out in the broaching work. FIG. 8 is a lateral sectional viewfor showing a state before the hub unit is carried out in the broachingwork. FIG. 9A and FIG. 9B are cross sectional views for showing a roughprocessing for forming the spline of the hub work for hub unitformation, wherein FIG. 9A shows a state before the broaching work, andFIG. 9B shows a state after the broaching work. FIGS. 10A to 10E arecharacteristic diagrams for showing deformation data of a spline hole ofthe hub work for the hub unit.

First, a member structure for conducting a broaching work will bedescribed with reference to FIG. 1. The hub unit work 103 which servesas a work before formation and processing of a female spline is disposedto turned up on a work stand 1, and a straight guide portion 2 b of atool 2 is inserted through a hole 3 a of the work 103. The work 103 isfixed to the work stand 1 on a lower surface of the flange 3 b which isa part separated from the portion 3 d plastically deformed by caulking(or clinching). The tool 2 consists of a part having a cutting edge 2 aand the straight guide portion 2 b having no cutting edge 2 a, and ismoved in a direction indicated by an arrow.

Since the degree of perpendicularity of the tool 2 with respect to theupper surface (a surface in contact with the lower surface of the flange3 b) of the work stand 1 in the axial direction is set with highprecision, a female spline having an excellent degree of perpendicularlyon the basis of the lower surface of the flange 3 b can be processed.This arrangement is effective for a hub unit for which high precision invibration of a brake is required.

A structure in which the hub unit work 103 (or the work 103) is disposedupside down is shown in FIG. 2. Description of the respective componentsin FIG. 2 is the same as that in FIG. 1 and will be omitted. The work103 is, when the female spline is formed and processed, received by aflat surface portion 1 a for plastically deforming by caulking (orclinching) of the work stand 1. This flat surface portion 1 a has beenprocessed in advance by cutting or coining. Since the degree ofperpendicularity in the axial direction of the tool 2 with respect to anupper surface (a surface in contact with the lower surface of the flange3 b) of the work stand 1 is set with high precision, the female splinewith high degree of perpendicularity based on the flat surface portion 1a for plastically deforming by caulking (or clinching) can be processed.Since the abutment between a flat surface portion of a constant velocityjoint to be connected to this hub unit 3 by bringing a female splineshaft for constituting an output shaft into engagement with the femalespline of the shaft 3 c and the flat surface portion 1 a can be set inan excellent state, this processing method is effective for a work whichis strict with abnormal sound from such an abutment surface.

Next, description will be made on a method according to a firstembodiment of the present invention, in which, before plasticallydeforming by caulking (or clinching), a hole is formed by cutting on theshaft portion 3 c of the hub 3 in the axial direction and then a bearingconstituted by an outer race 16, rolling members 18 and the inner raceelement 17 are fitted and attached on the shaft portion 3 c, thereafteran inner race element 17 being fixed by plastically deforming bycaulking (or clinching) from the outer end side of the shaft portion 3c, and then a semi-dry or dry broaching being conducted.

As shown in FIG. 3A, the hub shaft portion 3 c of the work 103 has beenformed by lathing in advance with the cylindrical hole 3 a through whichthe tool 2 is inserted. This hole 3 a has such a form that the diameterthereof becomes larger at a portion nearer a portion 3 d to beplastically deformed by caulking (or clinching) (upward in the drawing),that is, the diameter becomes larger for an estimated amount ofdeformation thereof by plastically deforming by caulking (or clinching)or an estimated amount of contraction caused by deformation byplastically deforming by caulking (or clinching) or by insertion of theinner race element 17 at a portion closer to the portion 3 d to beplastically deformed by caulking (or clinching).

This is because the inner diameter of the hole 3 a is contracted byplastically deforming by caulking (or clinching), as shown in FIG. 3B.If the inner diameter of the hole 3 a of the hub shaft portion 3 c issmaller than the outer diameter (the outer diameter of the straightguide portion 2 b) of the tool 2, the tip end of the tool 2 can not beinserted in the hole 3 a. To the contrary, when the inner diameter ofthe hole 3 a is excessively larger than the outer diameter of the tool2, the degree of concentricity of the tool 2 with respect to the hole 3a becomes low. Then, of the hole 3 a of the hub shaft portion 3 c, apart which is not influenced by plastically deforming by caulking (orclinching) or by insertion of the inner race element 17 is processed bycutting to have a high degree of concentricity, while a part which isgreatly influenced is processed to have a form that the inner diameterafter plastically deforming by caulking (or clinching) is not smallerthan the outer diameter of the tool 2.

A seal 11 is attached to the outer race 16 of the work 103, as shown inFIGS. 4A and 4B, in order to prevent chips from entering the bearingportion. A lip 11 a of the seal 11 can be formed to be twofold byutilizing a step portion of the inner race element 17. In thisstructure, chips are difficult to enter.

The structure for preventing chips is not limited to that describedabove. A detachable cap (not shown) may be provided. The cap is attachedto the work 103 before broaching and is removed after broaching. Thiscap is used repeatedly after the chips are taken off. The cap isparticularly effective for a work with an encoder formed of multipolarmagnet or a work to which a seal can not be attached. Even for a workwith a seal, the cap is used sometimes in order to prevent chips frombeing attached to the work itself.

Description will be made now on a process for forming the female splineon the hub shaft portion 3 c of the work 103 having the aboveconfiguration by broaching. As shown in FIG. 3B, the hole 3 a isprovided on the shaft portion 3 c of the hub 3, and, as shown in FIG. 5,the work 103 plastically deformed by caulking (or clinching) isconveyed, as indicated by an arrow, to be placed on the work stand 1. Inthis case, the tool 2 is retained by an upper chuck 4, and an upper lid5 serving as covering means is closed. In case of a work 103 for whichchips are produced in a large amount, for safety's sake, the cuttingedge 2 a of the tool 2 is given a brush 6 (cleaning means) so that thechips are absorbed by a vacuum tube 7. That is, a processing called acleaning is performed. This cleaning is required to be finished beforethe work 103 is placed on the work stand 1. It is possible to employ amethod that chips are to be detected by a sensor (not shown) and, whenthe sensor does not detect chips, cleaning is not carried out.

As shown in FIG. 6, when the work 103 is placed on the work stand 1, theupper chuck 4 which supports the tool 2 slowly descends. When the tool 2descends up to a position near the upper lid 5, the upper lid 5 isopened (unfolded) in a lateral direction (indicated by the arrow), andthe upper chuck 4 further descends so that the straight guide portion 2b of the tool 2 enters the hole 3 a of the hub shaft portion 3 c of thework 103, as described above. When the lower chuck 8 thereupon ascendsto come near a lower lid 9 which serves as the covering means, the lowerlid 9 is opened in the lateral directions (indicated by the arrows).When the upper chuck 4 slowly descends and the lower end portion of thetool 2 goes through the work 103 to reach the lower chuck 8, the lowerchuck 8 catches the lower end portion of the tool 2. The upper chuck 4,after confirming that the tool 2 is caught by the lower chuck 8,releases the tool 2.

In this case, in order to prolong the life of the tool 2, oil 20 issprayed on the tool 2 in the form of mist while the tool 2 slowlydescends. As shown in the same drawing, a nozzle 10 for spraying themist onto the tool 2 is provided above the work 103. When the tool 2passes by the nozzle 10, a groove of the cutting edge 2 a of the tool 2is sprayed with the mist of oil 20. An amount of the oil in this case is5 cc/h or less, in a state of semi-dry processed.

In case of a processing employing a tool having a sufficiently longlife, since the surface of the tool 2 is sufficiently smooth, thebroaching work is performed in a dry condition without no sprayed oil20. In this case, since no oil is used, oil does not permeate the work103 so that the processing environment is not stained with oil.

If the broaching work is conducted in a semi-dry or dry condition, thereis little need of performing a washing step using a spraying of, forexample, an air because of the oil used in the processing, unlike in aprocessing under a wet condition. Further, removal of chips is easierthan that in the wet processing.

The subsequent operations are as follows. First, as shown in FIG. 7,when the lower chuck 8 catches the lower end portion of the tool 2 andthe upper chuck 4 releases the tool 2, the lower chuck 8 descends at apredetermined speed. After releasing the tool 2, the upper chuck 4ascends, and the both ends of the upper lid 5 approach to each other indirections indicated by the arrows to close the upper lid 5. when thelower chuck 8 brings the tool 2 down below the work 103 as indicated bythe arrow, the lower lid 9 is closed.

A descending speed of the lower chuck 8 in this case, that is, a cuttingspeed in the broaching work is normally 3 m/min to 80 m/min. In thepresent embodiment, a comparatively high speed of 40 m/min to 80 m/minis employed. The reason for this is related to that the chips absorb theheat so that the tool 2 is hardly damaged.

Next, as shown in FIG. 8, when the tool 2 descends to pass by the work103 and a female spline 3 e is formed on the shaft portion 3 c, thelower lid 9 is closed in the directions indicated by the arrows, and atthe same time, the work 103 is carried out as indicated by the arrow. Onthe tool 2 which has descended, a cleaning operation is conducted forscraping off the chips attached onto the cutting edge 2 a of the tool 2by vibrating the brush 6, in the same manner as described above. Thescraped chips are absorbed by a vacuum tube 7. Upon completion of thecleaning operation, the lower chuck 8 pushed the tool 2 upward. When thetool 2 approaches the lower lid 9, the lower lid 9 is opened in adirection opposite to that indicated by the arrows. At the same time,the upper chuck 4 also descends and the upper lid 5 is opened. The tool2 is pushed upward at a low to medium speed, so that the tool 2 iscaused to ascend to reach the upper chuck 4. After it is confirmed thatthe tool 2 reaches the upper chuck 4 and the upper chuck catches thetool 2, the lower chuck 8 releases the tool 2. The lower chuck 8descends and the lower lid 9 is closed in directions indicated by thearrows. The chuck 4 which catches the tool 2 ascends at a high speed,and the upper lid 4 is closed. Then, the cleaning of the tool 2 isstarted, meanwhile another work is conveyed in. After that, theoperations shown in FIGS. 5 to 8 are repeated.

When the hub unit is divided into three areas depending on the positionof the lid, including an area higher than the upper lid 4, an area lowerthan the lower lid 9, and an area between the upper lid 4 and the lowerlid 9, the cleaning of the tool 2 can be carried out when there is nowork 103 and the broaching work after plastically deforming by caulking(or clinching) can be conducted without attaching chips onto the work103. In case of a spline processing which leaves very little chips, thebroaching work may be conducted in a structure having an upper lid onlyand no lower lid, or in a structure having a lower lid only and no upperlid. In case of the spline formation and processing producing no chip,the broaching work is be in some cases conducted in a structure with nolid.

As for a method of driving the chucks 4 and 9, the upper chuck 4 isdriven by an air cylinder and the lower chuck 9 by a mechanism having aservo motor and a ball screw combined with each other, respectively. Thedriving method is not limited to this. The upper chuck 4 or the lowerchuck 9 may be driven by oil pressure.

In the present embodiment, the female spline is processed by pulling thetool 2. However, the female spline may be formed and processed bypushing the tool 2. In addition, the present embodiment employs thescheme that the tool 2 is moved downward. However, a scheme that thetool 2 is moved upward may be employed.

The tool 2 for the broaching work shown in FIGS. 5 to 8 has the cuttingedge 2 with a helical groove. However, it is possible to use a toolhaving parallel grooves. However, as a groove of the tool 2, a helicalgroove can be processed continuously so that the female spline can beformed with precision with a helical groove. A cut amount is 5 μm to 50μm for one pitch from one cutting edge to another. In the presentembodiment, a cutting amount for one pitch is set as 10 μm to 30 μm. Amaterial of the tool 2 is high-speed steel or ultra-hard metal. Suchmaterial may be coated in some cases.

Further, in the present embodiment, the brush 6 is employed as thecleaning means for the tool 2. However, the cleaning means is notlimited to this. The cleaning may be conducted by spraying an air, usinga washing liquid, or another means.

Next, description will be made on a method according to a secondembodiment in which a rolling bearing comprising an outer race, rollingmembers and an inner race element is fitted and attached on a shaftportion 3 c′ of a hub 3′, and before the inner race element is fixed byplastically deforming by caulking (or clinching), that is, before a workfor a hub unit is assembled, a rough processing by broaching isconducted on the shaft portion 3 c′ of the hub 3′, and then a finishingprocessing is conducted by broaching after the inner race element isfixed by plastically deforming by caulking (or clinching). The finishingprocessing by broaching which is conducted after the inner race elementis fixed by plastically deforming by caulking (or clinching) is carriedout in the same manner as described above. In the following, descriptionwill be made on a case in which the rough processing is performed bybroaching prior to the plastically deforming by caulking (or clinching).

As shown in FIG. 9A, before the broaching work is conducted, a hole 3 f′is formed by cutting on the shaft portion 3 c′ of the hub work 3′ whichserves as a work for hub formation. This hole 3 f′ is not identical tothe hole 3 a which is shown in FIG. 3, but has a cylindrical form with auniform inner diameter. When a ring 12 is press-fitted onto the outerperipheral side of the shaft portion 3 c′ of this hub work 3′, the hole3 f′ is contracted toward the inner diameter side. An amount ofcontraction in this case is set as an amount which is obtained by addingan amount of deformation of the inner race element 17 (FIG. 3) when itis press-fitted to an amount of deformation by plastically deforming bycaulking (or clinching). An amount of contraction produced by thepress-fitting of the ring 12 is removed by broaching. When the ring 12is removed from the shaft portion 3 c′ of the hub work 3′ after therough processing by broaching, a hole 3 g′ for spline formation isobtained, as shown in FIG. 9B. This spline formation hole 3 g′ has aform in which the inner diameter thereof is larger at a part nearer aportion 3 d′ to be plastically deformed by caulking (or clinching) (thatis, gradually larger from lower to upper in the drawing). That is, thehole 3 g′ has a form which becomes larger at its part nearer the portion3 d′ to be plastically deformed by caulking (or clinching) for anestimated amount of contraction which may be caused by deformation byplastically deforming by caulking (or clinching) or press-fitting of theinner race element 17.

If the spline formation hole 3 g′ is shaped to have such a form by roughprocessing, it is possible to reduce an interference for the finishingwork by broaching after having effected plastically deforming bycaulking (or clinching), and to prolong the life of the tool. Or, it ispossible to omit the finishing work by broaching itself. In this case,the form of the hole 3 f′ is contracted by press-fitting of the ring 12.However, the form of the hole 3 f′ may be contracted by partiallychucking the outer diameter of the shaft portion 3 c′. In order tosmoothen the rough surface of the spline of the hub unit thus completed,a direction of moving the tool 2 in the rough processing is in somecases reversed to a direction of moving the tool 2 in the finishingwork. In addition, since a washing step is required in the roughprocessing prior to the assembling of the bearing, the rough processingis carried out in a wet condition, and the washing step is performedafter the processing.

FIGS. 10A through 10E show results of measurement which is performedplural times on the form of the female spline of the shaft portion 3 cof the hub 3 by means of a cylinder gauge at four points a, b, c and dof the spline formation hole 3 g in the axial direction, wherein FIG.10B shows a result of measurement performed after the rough processingby broaching (prior to the press-fitting of the inner race element);FIG. 10C shows a result of measurement after the press-fitting of theinner race element; and FIG. 10E shows a result of measurement after thefinishing work by broaching, respectively. In FIGS. 10A through 10E, theordinate represents the axial direction of the shaft portion 3 c and theabscissa represents an amount of deformation. From FIGS. 10B through10E, it is seen that, since a lower part of the spline formation hole 3g is swollen and extruded by the press-fitting of the inner race elementor by plastically deforming by caulking (or clinching) (particularly, byplastically deforming by caulking (or clinching)), an amount ofdeformation becomes greater at a lower part of the hub work 103 in theaxial direction.

Accordingly, it is effective if the data on the form of the femalespline shown in FIGS. 10A to 10E is obtained prior to the steps shown inFIGS. 3A, 3B and FIGS. 9A and 9B, and thereafter the forms for the stepsin FIGS. 3A, 3B and FIGS. 9A and 9B are determined. In both the firstand second embodiments, the axial force (the force for contracting theinner race element in the axial direction) of the hub unit hardlychanges before and after the broaching work. The axial force is reducedby several hundred kgf or around for the axial force of 5 to 10 tonf.Even under the worst of the circumstances estimated, it is calculatedthat the axial force is reduced by 5% at the maximum.

Note that, in case of the work 103 with an encoder, in order to preventchips from adhering, the encoder may be magnetized after a broachingwork. As for the processing method, Japanese Patent ApplicationLaid-Open Nos. 2001-287116 and 2001-269813 filed by a manufacturer of abroaching tool which is used in the experiments are referred.

As described above, according to a method of the present invention, ahole in a cylindrical form is provided on the shaft portion of a workfor a hub unit by cutting, a rolling bearing is fitted and attached onthe shaft portion, and, after an inner race thereof is fixed byplastically deforming by caulking (or clinching). In this case, a femalespline is formed on the hole by broaching, the female spline can beformed with precision without increasing the number of the processingsteps or the manufacturing cost.

Also according to another method of the present invention, the femalespline is roughly processed by broaching before the work for the hubunit is assembled, that is, before the rolling bearing is fitted andattached on the hub work and, after the rolling bearing is fitted andattached on the hub work and the inner race is fixed by plasticallydeforming by caulking (or clinching). In this case, the female spline isfinished by broaching, it is possible to reduce the processing cost forthe finishing work and to prolong the life of the tool, in addition toform the female spline with precision.

Further, according to a preferred embodiment of the present invention,it is possible to perform cleaning of the tool or, to prevent chips fromentering the bearing by attaching a seal to the work for the hub unit orproviding cleaning means or openable/closable covering means in thebroaching work.

1. A method of forming a female spline of a hub unit for supporting awheel, comprising the steps of: forming a work for a hub unit whichconsists of a hub integrally comprising a flange for attaching a wheeland a shaft portion formed with a hole extended in the axial directionand a rolling bearing fitted and attached on said shaft portion of thishub with an outer end of an inner race being fixed at the other end ofsaid shaft portion in the axial direction by plastically deforming bycaulking (or clinching); and subsequently, forming a female spline bysemi-dry or dry broaching on said hole of said shaft portion.
 2. Amethod of processing a female spline of a hub unit for supporting awheel according to claim 1, wherein said hole has the form that the sizethereof is greater at a portion nearer a portion plastically deformed bycaulking (or clinching) of said shaft portion for an estimated amount ofcontraction caused by the plastically deforming by caulking (orclinching) and press-fitting of the inner race element.
 3. A method offorming a female spline of a hub unit for supporting a wheel comprisingthe steps of: roughly processing a female spline by broaching on a holeof a work for a hub which integrally comprises a flange for attaching awheel and a shaft portion formed with said hole extended in the axialdirection; fitting and attaching a bearing on said shaft portion of thework for the hub and fitting and fixing the outer end of an inner raceof said shaft at the other end portion of said shaft portion in theaxial direction by plastically deforming by caulking (or clinching); andsubsequently, finishing the female spline by semi-dry or dry broachingon said hole of said shaft portion on which the spline is roughlyprocessed.
 4. A method of processing a female spline of a hub unit forsupporting a wheel according to claim 3, wherein the rough processing ofsaid female spline by broaching is carried out by press-fitting a ringon said shaft portion, or by chucking a part of said shaft portion so asto form the hole such that the size thereof is greater at a portionnearer a portion plastically deformed by caulking (or clinching) of saidshaft portion for an estimated amount of contraction caused byplastically deforming and press-fitting of an inner race element and thebroaching work is conducted in this state.
 5. A method of processing afemale spline of a hub unit for supporting a wheel according to claim 1,wherein said hub unit is provided with a seal or a detachable cap so asto perform a semi-dry or dry broaching work.
 6. A method of processing afemale spline of a hub unit for supporting a wheel according to claim 3,wherein said hub unit is provided with a seal or a detachable cap so asto perform a semi-dry or dry broaching work.
 7. A method of processing afemale spline of a hub unit for supporting a wheel according to claim 1,wherein cleaning means is employed for removing chips attached to a toolin the course of said semi-dry or dry broaching work.
 8. A method ofprocessing a female spline of a hub unit for supporting a wheelaccording to claim 3, wherein cleaning means is employed for removingchips attached to a tool in the course of said semi-dry or dry broachingwork.
 9. A method of processing a female spline of a hub unit forsupporting a wheel according to claim 1, wherein covering means which isopened only when the tool comes in or goes out is provided either one orboth on a side upper than the upper end of said hub unit and on a sidelower than a surface on which the hub unit is installed, and semi-dry ordry broaching work is performed by intercepting chips falling on the hubunit by means of this covering means.
 10. A method of processing afemale spline of a hub unit for supporting a wheel according to claim 3,wherein covering means which is opened only when the tool comes in orgoes out is provided either one or both on a side upper than the upperend of said hub unit and on a side lower than a surface on which the hubunit is installed, and semi-dry or dry broaching work is performed byintercepting chips falling on the hub unit by means of this coveringmeans.
 11. A method of forming a female spline of a hub unit forsupporting a wheel according to claim 1, wherein a direction of thebroaching work for roughly processing the female spline is the reverseof a direction of the finishing work of said female spline.
 12. A hubunit which is processed by a method according to claim
 1. 13. A hub unitwhich is processed by a method according to claim 11.